Recently, as portable electronic devices, electric vehicles, large-capacity power storage systems and the like have been developed, the need for large-capacity batteries is increasing. The lithium-sulfur battery is a secondary battery using a sulfur-based material having an S—S bond (Sulfur-Sulfur bond) as a positive electrode active material and using lithium metal as a negative electrode active material. The Lithium-sulfur battery has advantages in that sulfur, which is the main material of the positive electrode active material, is very rich in resources, is not toxic, and has a low atomic weight.
In addition, theoretical discharge capacity of the lithium-sulfur battery is 1672 mAh/g-sulfur, and its theoretical energy density is 2,600 Wh/kg. Since the energy density of the lithium-sulfur battery is much higher than the theoretical energy density of other battery systems currently under study (Ni-MH battery: 450 Wh/kg, Li—FeS battery: 480 Wh/kg, Li—MnO2 battery: 1,000 Wh/kg, Na—S battery: 800 Wh/kg), the lithium-sulfur battery is attracting attention as a battery having high energy density characteristics.
However, the shuttle phenomenon in which the intermediate lithium polysulfide is dissolved and moves between the positive electrode and the negative electrode shortens the lifetime of the battery and thus becomes a major obstacle to the commercialization of lithium-sulfur battery. In addition, it is difficult to increase the density of sulfur in the electrode, so that it is difficult to realize a battery having a high energy density unlike the theoretically known understanding and this is one of the problems to be overcome in lithium-sulfur battery.
In order to solve the above problems, a method of impregnating a carrier such as a polymer with sulfur is used. The most commonly used method is a method of causing elemental sulfur to be contained in a porous conductive medium such as mesoporous carbon (CMK-3). By using this method, the cycling characteristics could be improved to some extent while complementing the low conductivity of the sulfur. However, since the sulfur was not completely contained in the pores, the problem of elution of the polysulfide still occurred. In addition, since sulfur is impregnated in the carrier already synthesized, the impregnation amount of sulfur is limited depending on the pore volume of the carrier, and thus there was a problem that the final impregnation amount is difficult to be over 50%. Accordingly, a method for attaching an organic linker to the pure sulfur complex to increase the impregnation amount of sulfur was attempted, but there was a problem that the organic linker has been eluted in the electrolyte during the electrochemical reaction.
Therefore, it is necessary to develop a positive electrode active material for stable lithium-sulfur battery, which can increase the impregnation amount of sulfur and improve the problem of dissolving lithium polysulfide, and does not have the risk of elution of the carrier.    [Prior art document] Korean Patent Publication No. 2000-0074102, sulfur positive electrode with ultra-high capacity for lithium battery, preparation method thereof, and lithium battery using sulfur positive electrode.